It is known to provide an armrest on a door of a vehicle in a moveable manner so that the position of the armrest may be adjusted according to the position of the elbow of a vehicle occupant who may be of a particular build. For example, in a certain conventional armrest device, an armrest is attached to a door so as to be movable in a lateral direction of the vehicle (see Patent Document 1, for example). In other conventional armrest devices, an armrest is mounted on a door so as to be movable in a vertical direction with respect to the door (see Patent Document 2, for example), an armrest is mounted on a door so as to be movable in a fore and aft direction with respect to the door (see Patent Document 3, for example), and a rear end part of an armrest is rotatably mounted on a door so as to be rotatable around a rotational center line extending vertically with respect to the door (see Patent Document 4, for example).